1. Field of the Invention
The present invention is directed to an optical amplifier fiber or use in telecommunication systems and more particularly, an optical amplifier fiber having a large effective area and providing high absorption, linearity, and efficiency.
2. Technical Background
The continuous growth of bandwidth requirements in optical-based communication systems has resulted in a large demand for systems able to operate within several optical wavelength ranges including the S-band optical range, the C-band optical range, and the L-band optical range. The S-band is typically defined as the wavelengths between about 1465 nm and about 1525 nm, which lies below the C-band wavelength range which extends between about 1525 nm and about 1570 nm, which in turn lies just below the L-band wavelength range which extends between about 1570 nm and 1620 nm. In order to meet this explosive growth and demand for capacity in wavelength bandwidth in fiber optic transmission systems, system designers have begun to investigate those spectral regions lying beyond the conventional or C-band transmission band, including the aforementioned S-band and L-band wavelength ranges.
Erbium-doped fiber amplifiers are used to provide amplification in optical transmission systems, and particularly for deployment within those systems operating within the C-band wavelength range. Application of erbium doped fiber amplifiers within the telecommunication systems operating within the L-band wavelength range can be problematic in that lower excited-state population inversions are necessary to provide sufficiently flat gain spectra across the L-band wavelength range. Thus, longer lengths of fiber within the erbium-doped fiber amplifier or higher erbium concentrations therein are necessary to provide the same gain which would be provided within a given erbium doped fiber amplifier operating within the C-band wavelength range.
The longer lengths of fiber required in erbium doped fiber amplifiers utilized within the L-band wavelength range can result in a decrease in fiber efficiency and an increase in noise when compared with erbium doped fiber amplifier operating within the C-band wavelength range. Typically, the effective areas of erbium doped amplifier fibers are increased in an attempt to improve the xe2x80x9clinearityxe2x80x9d of the erbium doped fiber amplifiers. The reasoning for this approach has been that an increase in the effective area has the effect of enlarging the transverse optical power distribution in the fiber, thereby reducing the intensity of the optical power at any given point. This yields an erbium-doped fiber amplifier exhibiting a more linear material behavior. However, simply increasing the effective area of any particular erbium doped amplifier fiber by scaling the core diameter can have detrimental effects on optical performance including an increase in non-linear effects such as two-channel four-wave mixing. This is because the effective length of the deployed amplifier fiber may be increased in order to maintain absorption.
The spectroscopy of erbium within erbium doped fiber amplifiers operating within the L-band wavelength range thus poses several challenges with respect to designing the fiber amplifier to be used therein. These challenges include: (1) maximizing the effective area while simultaneously maintaining high absorption, (2) packaging amplifier modules with longer amplifier fibers required by the lower rate of gain while controlling fiber bend losses at longer wavelengths, (3) maintaining high absorption without significantly increasing concentration quenching, and (4) minimizing the intrinsically higher L-band noise figure.
This invention relates to an optical amplifier fiber that effects amplification of an optical signal within the L-band optical wavelength range. One aspect of the present invention relates to an optical waveguide amplifier fiber which comprises a core region having a relative refractive index xcex941 and an outer radius, the core region at least in part comprising Er2O3, and at least one other component selected from the group consisting of Al2O3, GeO2, Ga2O3, Ta2O3, P2O5, or a combination thereof; an inner clad surrounding the core region and having a relative refractive index percent xcex942 and an outer radius; and an outer clad surrounding the inner clad and having a relative refractive index percent xcex943. The relative refractive index percentages and radii of the core region, the inner clad and the outer clad are chosen so that the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 xcexcm to about 5.0 xcexcm; the outer radius of the inner clad within the range of from about 3.8 xcexcm to about 10.2 xcexcm. The relative amounts of Al2O3 and/or GeO2 and/or Ga2O3 within the core region, and the relative refractive index profile and percentages and radii of the core region, the inner clad and the outer clad are selected to provide an effective area of greater than or equal to about 38.6 xcexcm2, more preferably greater than about 44.0 xcexcm2, and most preferably greater than about 52.0 xcexcm2 at a wavelength of 1590 nm. Most preferably, the at least one other component comprises Ga2O3 in combination with P2O5.
The amounts of Er2O3, Al2O3 GeO2 and Ga2O3 within the core region, and the relative refractive index percent and radii of the core region, the inner clad and the outer clad are preferably selected to provide a pin array bending loss of less than or equal to about 0.11 dB, more preferably less than 0.09 dB, and most preferably less than 0.01 dB at a wavelength of 1590 nm.
The relative refractive index percent of the core region preferably increases linearly as the radius of the core region increases. The amplifier fiber also preferably exhibits an overlap factor of greater than or equal to about 50%, more preferably greater than about 70% at a wavelength of 1590 nm. In preferred embodiments, the amplifier fiber exhibits a step-index core.
Another aspect of the invention relates to an optical waveguide amplifier fiber which comprises a core region having a relative refractive index xcex941 and an outer radius, the core region at least in part comprising Er2O3, and at least one other component selected from the group consisting of Al2O3, GeO2, Ga2O3, Ta2O3, P2O5, or a combination thereof; an inner clad surrounding the core region and having a relative refractive index percent xcex942 and an outer radius; and an outer clad surrounding the inner clad and having a relative refractive index percent xcex943. The relative refractive index percentages and radii of the core region, the inner clad and the outer clad are chosen so that the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 xcexcm to about 5.0 xcexcm; the outer radius of the inner clad within the range of from about 3.8 xcexcm to about 10.2 xcexcm. The amounts of Al2O3 and/or GeO2 and/or Ga2O3 within the core region, and the relative refractive index percentages and radii of the core region, the inner clad and the outer clad are selected to provide an effective area of greater than or equal to about 38.6 xcexcm more preferably greater than about 44.0 xcexcm2, even more preferably greater than about 52.0 xcexcm2, and most preferably greater than about 63 xcexcm2 at a wavelength of 1590 nm. Most preferably, the at least one other component comprises Ga2O3 in combination with P2O5.
The amounts of Er2O3, Al2O3, GeO2 and Ga2O3 within the core region, and the relative refractive index percent and radii of the core region, the inner clad and the outer clad are preferably selected to provide a pin array bending loss of less than or equal to about 0.11 dB, more preferably less than 0.09 dB, and most preferably less than 0.01 dB at a wavelength of 1590 nm.
The relative refractive index percent of the core region preferably increases linearly as the radius of the core region increases. The amplifier fiber also preferably exhibits an overlap factor of greater than or equal to about 50%, more preferably greater than about 70% at a wavelength of 1590 nm. In preferred embodiments, the amplifier fiber exhibits a step-index core.
The amplifer fibers disclosed herein may be employed as fibers in a telecommunication system, for example such a system that comprises one or more transmitters adapted to transmit an optical signal, a waveguide transmission fiber in optical communication with the transmitters; and a receiver adapted to receive the optical signal.
Another aspect of the invention relates to an optical waveguide amplifier fiber which comprises a core region having a relative refractive index percent and an outer radius, the core region at least in part comprising Er2O3, Al2O3, GeO2 and Ga2O3 an inner clad surrounding the core region and having a relative refractive index percent and an outer radius; and an outer clad surrounding the inner clad and having a relative refractive index percent. The relative amounts of Al2O3 and/or GeO2 and/or Ga2O3 within the core region, and the relative refractive index profile and percentages and radii of the core region, the inner clad and the outer clad are selected to provide an effective area of greater than or equal to about 38.6 xcexcm2, more preferably greater than about 44.0 xcexcm2, and most preferably greater than about 52.0 xcexcm2 at a wavelength of 1590 nm. Most preferably, the at least one other component comprises Ga2O3 in combination with P2O5.
The amounts of Er2O3, Al2O3, GeO2 and Ga2O3 within the core region, and the relative refractive index percent and radii of the core region, the inner clad and the outer clad are preferably selected to provide a pin array bending loss of less than or equal to about 0.11 dB, more preferably less than 0.09 dB, and most preferably less than 0.01 dB at a wavelength of 1590 nm.
In a first embodiment, an optical waveguide fiber amplifier comprises a core region having a relative refractive index percent and an outer radius, wherein the core region at least in part comprises Er2O3 and at least one other component selected from the group consisting of Al2O3, GeO2, Ga2O3, Ta2O3, P2O5, or combinations thereof. In one embodiment, the other dopant components in the core region include both Ga2O3 and P2O5. The optical amplifier fiber preferably also contains SiO2, and more preferably is comprised predominately of SiO2. The fiber also comprises an inner clad surrounding the core region and having a relative refractive index percent and an outer radius, and an outer clad surrounding the inner clad and having a relative refractive index percent. The relative refractive index percentages and radii of the core region, inner clad and the outer clad are preferably chosen from the following ranges: the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 xcexcm to about 5.0 xcexcm; and, the outer radius of the inner clad within the range of from about 3.8 xcexcm to about 10.2 xcexcm. The relative refractive index percentages and radii of the core region, inner clad and outer clad are preferably selected to provide an effective area of greater than or equal to about 38.6 xcexcm at a wavelength of about 1590 nm. More specifically, the invention relates to an erbium-doped optical amplifier fiber operating in the L-band optical wavelength range and having a large effective area while minimizing effective length, and reducing the associated noise, and maintaining high efficiency sufficient bandwidth carrying capacity.
In a second embodiment, an optical waveguide fiber amplifier comprises a core region having a relative refractive index percent and an outer radius, wherein the core region at least in part comprises SiO2, Er2O3, Al2O3, GeO2, Ta2O5, P2O5 and/or Ga2O3. The optical amplifier fiber also comprises an inner clad surrounding the core region and having a relative refractive index percent and an outer radius, and an outer clad surrounding the inner clad and having a relative refractive index percent. The relative refractive index percentages and radii of the core region, the inner clad and the outer clad are selected to provide an overlap factor of greater than or equal to about 50%, and an effective area of greater than or equal to about 36.0 xcexcm2 at a wavelength of 1590 nm.
The present invention also includes optical communication systems employing the optical waveguide fiber amplifiers in accordance with the embodiments described above.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. An exemplary embodiment of the segmented core refractive index profile of the present inventive optical waveguide fiber amplifier is shown in the figures.